From: Ming Lei <ming.lei@redhat.com>
Date: Fri, 11 Sep 2020 18:41:14 +0800
Subject: blk-mq: always allow reserved allocation in hctx_may_queue
Patch-mainline: v5.10-rc1
Git-commit: 285008501c65a3fcee05d2c2c26cbf629ceff2f0
References: bsc#1193787

NVMe shares tagset between fabric queue and admin queue or between
connect_q and NS queue, so hctx_may_queue() can be called to allocate
request for these queues.

Tags can be reserved in these tagset. Before error recovery, there is
often lots of in-flight requests which can't be completed, and new
reserved request may be needed in error recovery path. However,
hctx_may_queue() can always return false because there is too many
in-flight requests which can't be completed during error handling.
Finally, nothing can proceed.

Fix this issue by always allowing reserved tag allocation in
hctx_may_queue(). This is reasonable because reserved tags are supposed
to always be available.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Cc: David Milburn <dmilburn@redhat.com>
Cc: Ewan D. Milne <emilne@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Daniel Wagner <dwagner@suse.de>
---
 block/blk-mq-tag.c |    3 ++-
 block/blk-mq.c     |    5 +++--
 2 files changed, 5 insertions(+), 3 deletions(-)

--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -59,7 +59,8 @@ void __blk_mq_tag_idle(struct blk_mq_hw_
 static int __blk_mq_get_tag(struct blk_mq_alloc_data *data,
 			    struct sbitmap_queue *bt)
 {
-	if (!data->q->elevator && !hctx_may_queue(data->hctx, bt))
+	if (!data->q->elevator && !(data->flags & BLK_MQ_REQ_RESERVED) &&
+			!hctx_may_queue(data->hctx, bt))
 		return BLK_MQ_NO_TAG;
 
 	if (data->shallow_depth)
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1105,10 +1105,11 @@ static bool __blk_mq_get_driver_tag(stru
 	if (blk_mq_tag_is_reserved(rq->mq_hctx->sched_tags, rq->internal_tag)) {
 		bt = rq->mq_hctx->tags->breserved_tags;
 		tag_offset = 0;
+	} else {
+		if (!hctx_may_queue(rq->mq_hctx, bt))
+			return false;
 	}
 
-	if (!hctx_may_queue(rq->mq_hctx, bt))
-		return false;
 	tag = __sbitmap_queue_get(bt);
 	if (tag == BLK_MQ_NO_TAG)
 		return false;